Bag house filtration systems are primarily used in industrial environments to remove dust, and contaminants and other particles from an air stream such as in coal fired power plants. Bag house filtration systems circulate air through the wall(s) of a bag which collects or reclaims the particles. The bag, typically formed from a textile or media, performs as both a barrier to the particles and a conduit for air to pass through. The dual functionality required for modern filter media have focused on three objectives: effectively remove particles from the air, reduce the energy required to circulate air, and to enhance the cleaning of the bags as needed.
The ability to clean the air stream circulated through the bag house systems has been referred to in the art as filtration efficiency. A measure of filtration efficiency is the ratio of downstream (output) particle concentration compared to the upstream (input) particle concentration that has passed through the bag or filter media. As more particulate is collected on the surface of the filter media the energy required to transport air through the bag (or any filter media) also increases, thus the balance between effective air cleaning and energy usage is delicate.
Energy usage in a bag house system is related to the pressure drop through the bags or filter media. Pressure drop, as used herein, refers to the difference in air pressure between each side of a filter media when there is air flow through the filter media. A low pressure drop media requires less energy to push air through the bag lessening the overall energy consumption of the system. Over time a phenomena referred to as filter cake formation occurs where the bag collects particles on its surface. As the filter cake increases in thickness the pressure drop of the filtration system increases, also increasing the energy requirements of the bag house filtration system. There is a continued need for a high temperature air filter having low pressure drop and high filtration efficiency.